Recent studies have indicated that opioid peptides are present within the testis and appear to serve as paracrine or autocrine regulators of testicular function. The principal investigator has now obtained new evidence for the expression of an mRNA for the opioid peptide precursor, proenkephalin, in the rat testis. The size of this testicular preproenkephalin mRNA is unique, being substantially larger than preproenkephalin mRNAs from any tissue previously examined. The specific aims of this proposal are to: (1) identify the cell types that express preproenkephalin-like mRNA and proenkephalin-derived peptides in rat testis; (2) characterize the primary translation product derived from testicular preproenkephalin-like mRNA; (3) determine the nucleotide sequence of preproenkephalin-like mRNA in the rat testis; (4) characterize the peptide products derived from the testicular preproenkephalin-like protein. These studies will define the nature of preproenkephalin mRNA and protein in the rat testis and will be essential for future projected investigations into the cellular sites of action and the hormonal regulation of proenkephalin gene expression in this tissue.